Apparatus and method for measuring oxygen diffusing capacity and heating packet

ABSTRACT

The present invention provides a measuring apparatus and method for measuring the quantity of ventilation, whereby the quantity of ventilation correlates to the heating characteristics. [The present invention is also] able to measure the quantity of ventilation of a gas permeable packing material used in heating packets in a short period of time, regardless of the type or pore diameter of the packing material. The present invention provides heating packets displaying stable heating characteristics. In the present invention, one surface of a gas permeable packing material is exposed to the atmosphere, while the opposite surface is scavenged with a carrier gas which does not include oxygen. The present invention measures the oxygen diffusing capacity, [as the diffusion of oxygen] from the atmosphere through the gas permeable packing material, by measuring the concentration of oxygen in the carrier gas after scavenging. Also, the present invention provides body, pocket, and shoe heating packets wherein the quantity of ventilation is regulated by the oxygen diffusing capacity.

TECHNICAL FIELD

The present invention relates to a method and apparatus for measuringthe gas permeability of the gas permeable packing material, and aheating packet using a gas permeable packing material with the quantityof ventilation regulated by oxygen diffusing capacity. The presentinvention relates to an apparatus for measuring oxygen diffusingcapacity and a method for measuring oxygen diffusing capacity, formeasuring the gas permeability of a gas permeable packing material usedin pocket heaters and oxygen scavengers, and a heating packet withquantity of ventilation regulated by oxygen diffusing capacity.

BACKGROUND ART

Up to now, heating packets have been made of a heat generatingcomposition, composed mainly of oxidative metal powders which generateheat upon contact with the oxygen in the air, which are enclosed in agas permeable inner pouch, then sealed within an airtight outer pouch.These heating packets are used as medical devices, or as disposablepocket heaters for body warming. Furthermore, heating packets used formaintaining body temperature include the following: body heating packetsused on the shoulders and lower back, pocket heating packets used inpockets and gloves, and shoe heating packets inserted in shoes.

The quantity of the heat generating composition, the proportions of theconstituents of the heat generating composition, and the quantity ofventilation of the inner pouch of these heating packets are establishedaccording to usage, so that the heating packet attains the desiredmaximum temperature, time required to reach the desired temperature(rise time), and duration of heat production.

This heat generating composition is a mixture of oxidative metal powder,activated carbon, inorganic electrolytes, water, and so forth.Generally, iron powder is used as the oxidative metal powder. The heatgenerating composition generates heat when the oxidative metal powderbecomes a metal oxide upon contact with the oxygen in the air.

Also, the gas permeable packing material used as the inner pouch may beone of the following: (1) a gas impermeable sheet wherein comparativelylarge holes, with equivalent diameters of 0.03-0.5 mm, are formed usingneedles or electric discharge; (2) nonwoven fabric, with limited gaspermeability, formed by the superposition and thermocompression bondingof synthetic fibers of polyethylene, polypropylene, or the like; or (3)material (fine pored film) formed by dispersing a fine powder of calciumcarbonate, barium sulfate, or the like in synthetic resin such as moltenpolyethylene, polypropylene, or the like, forming this into a film, thendrawing the film to form fine pores with equivalent diameters of 10 μmor less. Furthermore, nonwoven fabric or the like may be laminated onthese gas permeable packing materials.

Here, the heating characteristics of the heating packet can becontrolled by methods such as the following: the method of adjusting theproportions of the constituents of the heat generating composition asnoted above; the method of controlling the quantity of oxygen suppliedto the heat generating composition. Furthermore, the heatingcharacteristics can be controlled by both the adjustment of the heatgenerating composition and the control of the quantity of ventilationthrough the gas permeable packing material. However, the heatingcharacteristics are generally set by adjusting the quantity ofventilation through the gas permeable packing material used as the Innerpouch. Known methods are employed for measuring the quantity ofventilation through these gas permeable packing materials. Proposedmethods include the following: (1) methods using the Gurley permeabilitymeasuring method (JIS P 8117) (Japanese Patent Publication No. 7-90030,Japanese Patent Laid-open Publication No. 8-80317), (2) methods usingthe Frazier-type tester (JIS L 1018, JIS L 1096) (Japanese PatentLaid-open Publication No. 7-67907), and (3) methods using the watervapor permeability measuring method (JIS Z 0208) (Japanese PatentLaid-open Publication No. 7-124192, Japanese Patent Laid-openPublication No.8-92075). These methods are used in the design andquality control of the heating characteristics of heating packets.

Also, the official methods for measuring the heating characteristics ofheating packets are the testing methods prescribed in the JapaneseIndustrial Standards (JIS S 4100). According to these, the heatingcharacteristics are measured using a temperature measuring apparatusprescribed in JIS S 4100, under conditions of 20° C. externaltemperature and 65% relative humidity. The regulations prescribe thatthe heating characteristics be expressed as the time from the start ofthe heating operation until a temperature of 40° C. is reached (risetime), the maximum temperature reached (maximum temperature), and thetime for which temperatures of 40° C. or more are maintained(continuation time).

The heating packet generates heat because of the oxidative reactionwhich occurs when oxygen is supplied by the oxygen in the air passingthrough the fine holes in the gas permeable packing material over a longperiod of time and the oxygen and oxidative metal powder (iron powder isa representative metal powder) come into contact.

However, the aforementioned method for measuring the quantity ofventilation depends on the size of the pores, form of the pores, type ofmaterial, and composition of the gas permeable packing material formingthe inner pouch. There is no correlation between the measured value forthe quantity of ventilation and the temperature characteristics. As aresult, a problem is that the design and quality control for the heatingpacket are not adequate.

The aforementioned (1) Gurley gas permeability measurement method isconstituted so that the weight of the gas chamber of the measurementapparatus operates as a pressure difference between the front and backof the gas permeable packing material. This is specifically a method formeasuring the time necessary for a constant volume of gas to passthrough the gas permeable packing material.

This measurement method is able to make the measurements for a packingmaterial having relatively large pores, with equivalent diameters of0.03-0.5 mm and formed with pins or electrical discharge, in severalseconds to several minutes. However, a long period of time, such asseveral thousand to ten thousand seconds or more, is necessary formeasuring a gas permeable packing material having a large number ofsmall holes, such as a gas permeable packing material formed bydispersing a fine powder of calcium carbonate, barium sulfate, or thelike in synthetic resin such as molten polyethylene, polypropylene, orthe like, forming this into a film, then drawing the film to form finepores with equivalent diameters of 10 μm or less. Moreover,reproducibility is poor because the measured values fall outside therange (2-1800 seconds/100 ml) of the Gurley gas permeability measurementmethod itself.

Furthermore, there are cases where the same heating characteristics aregiven even when the Gurley gas permeability measurement values differmarkedly depending on the type of gas permeable packing material. Theproblem is that there is no correlation between the values measured forthe quantity of ventilation and heating characteristics. Also, the (2)method using a Frazier-type tester is a method for measuring mainly thegas permeability of textiles. This is a method which applies a pressuredifference of 12.7 mmH₂O between the front and back surfaces of the gaspermeable packing material. This method can be applied to themeasurement of a gas permeable packing material with large air holes.However, the quantity of ventilation is too small in the case of a gaspermeable packing material with fine pores of 5 μm or less and thismeasurement method cannot measure outside of Its range (0.3-400cc/cm²/sec). Furthermore, (3) the water vapor permeability measurementmethod is a method for finding water vapor permeability from the amountof water vapor which diffuses through the gas permeable packing materialunder conditions of moisture saturation, without applying a pressuredifference between the front and back surfaces of the gas permeablepacking material. This appears to be a superior method. However,depending on the type of the gas permeable packing material, there is nocorrelation between the heating characteristics and the measured valueof water vapor permeability. This applies in particular to the case of agas permeable packing material which absorbs moisture or a gas permeablepacking material having fine pores. Because of these issues, there is astrong desire for the development of a method for measuring the quantityof ventilation, which can measure the quantity of ventilation quicklyand precisely, regardless of the type of gas permeable packing material,and with which a correlation with heating characteristics is attained.

Also, because of the lack of correlation between heating characteristicsand quantity of ventilation of the gas permeable packing material usedas the inner pouch as noted above, it has heretofore been impossible todesign the heating characteristics with good precision and to havequality control for body heating packets, pocket heating packets, orshoe heating packets.

For this reason, it is desirable to develop heating packets having thedesired heating characteristics and having stable heatingcharacteristics.

In the case of shoe heating packets, the only heating packets availablediffer markedly from the desired heating characteristics, despite theextreme market requirements, for the aforementioned reasons. For thisreason, it is desirable to develop heating packets having the desiredheating characteristics and having stable heating characteristics.Therefore, it is an object of the present invention to provide a methodfor measuring the quantity of ventilation which correlates to heatingcharacteristics and which can measure the quantity of ventilationquickly and precisely, regardless of the type of gas permeable packingmaterial. It is another object of the present invention to provide anapparatus for measuring the quantity of ventilation which correlates toheating characteristics and which can measure the quantity ofventilation quickly and precisely, regardless of the type of gaspermeable packing material.

Furthermore, it is another object of the present invention to provide aheating packet having the desired heating characteristics and havingstable heating characteristics. It is another object of the presentinvention to provide various types of heating packets, as body warmers,pocket warmers, and shoe warmers.

DISCLOSURE OF THE INVENTION

As a result of their diligent research into solving these problems, theinventors discovered a correlation between the heating characteristicsof the heating packet and the oxygen diffusing capacity. Theyaccomplished this by placing a gas permeable packing material with onesurface exposed to the atmosphere and scavenging the other surface witha carrier gas which does not include oxygen, and finding the oxygendiffusing capacity, which is the quantity of the oxygen gas in theatmosphere passing through the gas permeable packing material anddiffusing into the carrier gas, as the standard of gas permeability.Furthermore, they discovered that they could use the gas permeability,determined with the oxygen diffusing capacity as a standard, anddetermine the quantity of ventilation appropriate for body warmers,pocket warmers, and shoe warmers, whereby they attained heating packetswith stabilized heating characteristics and arrived at the presentinvention.

Specifically, the present invention is a method for measuring the oxygendiffusing capacity of a gas permeable packing material, by exposing onesurface of a gas permeable packing material to the atmosphere andscavenging the other surface with a carrier gas which does not includeoxygen, then measuring the gas permeability of the gas permeable packingmaterial from the concentration of oxygen gas in the carrier gas afterscavenging.

Also, the present invention is an apparatus for measuring the oxygendiffusing capacity of a gas permeable packing material which is provideda diffuser, wherein the oxygen gas in the atmosphere diffuses into thecarrier gas through the gas permeable packing material, when one surfaceof a gas permeable packing material is exposed to the atmosphere and theother surface is scavenged with the aforementioned carrier gas.

Furthermore, the present invention is a body warming heating packetcomprising a heat generating composition, which generates heat uponcontact with oxygen in the air, within a gas permeable inner pouch andfurther sealed within a non-gas permeable outer pouch, wherein onesurface of the inner pouch is a gas permeable packing material with anoxygen diffusing capacity corresponding to a range of 1100±220 Nl/m² 24h(same below) measured when one surface of a gas permeable packingmaterial is exposed to the atmosphere and the other surface is scavengedwith the aforementioned carrier gas at a flow rate of 0.193 Nl/cm² h perunit area of the gas permeable packing material, under conditions of 20°C. and 65% relative humidity.

Furthermore, the present invention is a pocket warming heating packetcomprising a heat generating composition, which generates heat uponcontact with oxygen in the air, within a gas permeable inner pouch andfurther sealed within a non-gas permeable outer pouch, wherein onesurface of [the inner pouch] is a gas permeable packing material with anoxygen diffusing capacity corresponding to a range of 1600±350 Nl m²24hmeasured when one surface of a gas permeable packing material is exposedto the atmosphere and the other surface is scavenged with theaforementioned carrier gas at a flow rate of 0.193 Nl/cm² h per unitarea of the gas permeable packing material, under conditions of 20° C.and 65% relative humidity.

Additionally, the present invention is a shoe warming heating packetcomprising a heat generating composition, which generates heat uponcontact with oxygen in the air, within a gas permeable inner pouch andfurther sealed within a non-gas permeable outer pouch, wherein onesurface of [the inner pouch] is a gas permeable packing material with anoxygen diffusing capacity corresponding to a range of 5500±1100 Nl/m²24h measured when one surface of a gas permeable packing material isexposed to the atmosphere and the other surface is scavenged with theaforementioned carrier gas at a flow rate of 0.193 Nl/cm² h per unitarea of the gas permeable packing material, under conditions of 20° C.and 65% relative humidity.

In the present invention, the carrier gas which does not include oxygenis preferably nitrogen, but other gases such as argon, helium, carbondioxide, or the like may also be used without any particularrestrictions. Moreover, in the present invention, the phrase “notincluding oxygen” does not exclude the inclusion of oxygen at a levelwhich does not influence the measurement of gas permeability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a cross sectional view of a diffuser;

FIG. 2 is a block diagram showing the principle of the apparatus formeasuring oxygen diffusing capacity relating to the present invention;

FIG. 3 is an example of the inner pouch using the gas permeable packingmaterial having small pores; (a) is a plane diagram and (b) is a crosssectional view at line 3-3′;

FIG. 4 is an example of the inner pouch using the gas permeable packingmaterial having small pores in part;

FIG. 5 is an example of an inner pouch using the gas permeable packingmaterial wherein pin holes are concentrated in the center;

FIG. 6 is an example of an inner pouch with a back seal and using thegas permeable packing material having pin holes in the center; (a) is aplane diagram and (b) is a cross sectional view at line 6-6′;

FIG. 7 is a diagram showing the properties of the relationship betweenthe maximum temperature and the oxygen diffusing capacity in embodiments1-9;

FIG. 8 is a diagram showing the properties of the relationship betweenthe rise time and the oxygen diffusing capacity in embodiments 1-9;

FIG. 9 is a diagram showing the properties of the relationship betweenthe continuation time and the oxygen diffusing capacity in embodiments1-9;

FIG. 10 is a diagram showing the properties of the relationship betweenthe maximum temperature and the oxygen diffusing capacity in embodiments10-13;

FIG. 11 is a diagram showing the properties of the relationship betweenthe rise time and the oxygen diffusing capacity in embodiments 10-13;

FIG. 12 is a diagram showing the properties of the relationship betweenthe continuation time and the oxygen diffusing capacity in embodiments10-13;

FIG. 13 is a diagram showing the properties of the relationship betweenthe maximum temperature and the oxygen diffusing capacity in embodiments14-21;

FIG. 14 is a diagram showing the properties of the relationship betweenthe rise time and the oxygen diffusing capacity in embodiments 14-21;

FIG. 15 is a diagram showing the properties of the relationship betweenthe continuation time and the oxygen diffusing capacity in embodiments14-21; and

FIG. 16 is a diagram showing the properties of the relationship betweenthe maximum temperature and water vapor permeability in embodiments14-21.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is applied to the measurement of the quantity ofventilation through a gas permeable packing material used in heatingpackets and oxygen scavengers. Also, the present invention is applied tobody warmers, pocket warmers, and shoe warmers wherein the quantity ofventilation is regulated by the oxygen diffusing capacity.

The method and apparatus for measuring oxygen diffusing capacityrelating to the present invention can be used for measuring the quantityof ventilation for highly gas permeable packing materials, as well aspacking materials with very low gas permeability, in a short period oftime. With the method and apparatus for measuring oxygen diffusingcapacity relating to the present invention, the front and back surfacesof the gas permeable packing material are maintained under equal totalpressure conditions and oxygen diffuses therethrough because of thedifference in partial pressure of the oxygen in the gases contactingthese surfaces. This quantity of oxygen is measured-with the presentinvention. The method and apparatus relating to the present inventionare constituted so that measurement is made under conditions where thedifference in total pressure between the two surfaces becomes nearlyzero.

The surface of the gas permeable packing material which is in contactwith the air is kept in continuous contact with fresh air, specificallyin a state where the surface in contact with air is exposed to theatmosphere. Meanwhile, it is required that fresh nitrogen be continuallysupplied to the surface of the gas permeable packing material which isin contact with nitrogen, so that the difference in oxygen partialpressure remains constant even in the case where oxygen diffusestherethrough. Specifically, methods for the continual supply and exhaustof nitrogen are used.

The present invention is explained more specifically using the drawings.

FIG. 1 shows an example of a cross sectional view of the diffuser of theapparatus for measuring oxygen diffusing capacity relating to thepresent invention. FIG. 2 shows an example of the apparatus formeasuring oxygen diffusing capacity wherein two diffusers areestablished in a parallel configuration.

In FIG. 1, the diffuser 1 comprises a chamber 2 and a cover portion 3.The chamber 2 is cylindrical and a nitrogen gas supply tube 5 isestablished in the central portion thereof. An exhaust tube 6 isestablished in an area near the outer perimeter of the chamber. Withinthe chamber, a cylindrical partition barrier 7 is established in orderto prevent the nitrogen gas from being directly exhausted (short pass).The cover portion 3 comprises metal frames 8, 9 and backing sheets 10,11. An airtight seal with the chamber is maintained by means of aring-shaped sheet backing 13. A hollow portion equivalent to themeasured surface 12 of the gas permeable packing material 4 is formed inboth the frames 8, 9 and backing sheets 10, 11.

The gas permeable packing material 4 is held between the backing sheets10, 11; the entirety is affixed between the base frame 14 and coverportion 3, which are screwed together with the bolt 15 and nut 16.

With the apparatus in this state, nitrogen gas flows at a constant flowrate from the nitrogen gas supply tube 5. The oxygen diffusing capacityof the gas permeable packing material can be measured by measuring theconcentration of oxygen in the gas flowing out from the exhaust tube 6.FIG. 2 shows the constitution of the apparatus for measuring oxygendiffusing capacity having a series of two diffusers. The nitrogen gas issupplied to the diffuser 1 from a pressure reducing valve 17 via thenitrogen gas flow controller 18. The exhaust gas of the diffuser 1 isexhausted via the oxygen concentration detector 19 and then the purgeline 21. FIG. 2 also shows the case of measuring oxygen concentrationusing one gas chromatograph 23. The gas flow path from the diffuser 1 isconnected to the gas chromatograph 23 via a branched portion 20 andswitching valve 22. A gas aspirator 25 is connected to the rear of thegas sampling portion 24 of the gas chromatograph 23. The apparatus isthereby set to attain a constant flow rate even in the event of flowpath resistance from the branched portion 20 to the gas sampling portion24.

In addition to the structure and form of diffuser shown in FIG. 1, thepresent invention can also have a diffuser wherein the chamber is asquare box or elliptical cylinder. Also, in FIG. 1, the scavenging gas,which is nitrogen gas, flows from the central area of the chamber towardthe periphery. It is also possible for the scavenging gas to flow fromthe periphery to the center, or in the case of a box-shaped chamber, toflow from one end to the opposite end, parallel to the measured surface.Chamber size corresponds to the size of the measured surface of the gaspermeable packing material to be measured. Chamber size is not limitedso long as the nitrogen gas uniformly scavenges the measured surface ofthe gas permeable packing material, and the gas In the chamber isreplaced in a short period of time.

There are no restrictions on the type and shape of frame, which can besquare, rectangular, or round. The size and form of the frame are notrestricted if a measured surface, of sufficient area to represent thegas permeability of the gas permeable packing material, is attained. Ifthe area of the measured surface is too small, the precision of themeasurement is reduced and if too large, it becomes difficult tomaintain the flatness of the measured surface. As a result, the area isusually 2-300 cm², and preferably 10-100 cm².

The backing sheet may comprise a backing of synthetic resin or rubberbacking, having the elasticity of rubber, so as to prevent gas leakageeven in the case of the gas permeable packing material having a slightlyirregular surface. FIG. 1 shows an example of a structure wherein thechamber and cover portion can be separated, but it is also possible forthe chamber portion and cover portion to be formed as a unit. Also, itis possible to screw the gas permeable packing material to the chamberin a single operation using a pneumatic cylinder, lever, or rotatinghandle.

Moreover, in the case where the gas permeable packing material ismounted on the chamber, it is preferably mounted in accord with thestate of use in a heating packet. Specifically, the packing material ispreferably mounted on the chamber in such a manner that the surfacewhich corresponds to the outside of the inner pouch is exposed to theatmosphere, and the surface which corresponds to the inner surface ofthe inner pouch becomes the surface scavenged with nitrogen.

A gas chromatograph or an oxygen densitometer using an oxygen gas sensorcan be used for measuring the oxygen concentration. In the case of usingeither instrument, it is necessary to use a flow path structure withlittle fluid resistance, in order that no pressure difference occurbetween the atmosphere and the interior of the diffuser chamber. Forthis reason, a method established close to the exhaust tube portionwithin the chamber, or a method established directly beyond the exhausttube portion, is used when taking measurements using an oxygen gassensor. In the case of taking measurements with a gas chromatograph, itis preferable maintain conditions so that no pressure difference occursbetween the chamber and atmosphere, for example, by using a method ofaspirating gas at a constant flow rate to the sampling portion of thegas chromatograph.

Furthermore, measurement efficiency can be improved as follows. Thedisposition of two parallel diffusers, as shown in FIG. 2, makes itpossible to take measurements with one series, while replacing thesample in the other.

Otherwise, the measured surface can be made relatively large and themeasured value can be calculated as a representative value for the gaspermeable packing material, depending on the distribution of the airholes in the gas permeable packing material, for example, when the airholes are continuous like a dotted line or the holes are concentrated inthe central portion.

The nitrogen gas supplied to the diffuser is preferably highly purifiednitrogen gas, to permit high precision measurement of a gas permeablepacking material with little oxygen diffusing capacity. Also, if theamount of nitrogen gas supplied is too large, this can cause deformationor oscillation of the sample surface. If too small, the concentration ofthe oxygen in the nitrogen gas becomes high because of oxygen diffusionand the difference in oxygen partial pressure between the front and backof the gas permeable packing material becomes undesirably small. As aresult, nitrogen gas is usually supplied at 50-2000 ml/cm² h, andpreferably 100-500 ml/cm² h, per unit area of the measured surface ofthe gas permeable packing material.

The flow rate of nitrogen supplied can be controlled using a flow meterand needle valve. Otherwise, a mass flow controller can control the flowrate with good precision and is therefore convenient.

In the diffuser, a difference between the pressure on the side exposedto the atmosphere and the pressure within the chamber may result in aflow of oxygen which is not a result of diffusion from the atmosphereside into the chamber, or a flow of nitrogen from the chamber to theatmosphere side. This is as a result of a viscous flow occurring on thebasis of the pressure difference for a gas permeable packing materialwith large pore diameters. Consequently, while this may vary dependingon pore diameter, the apparatus is usually constituted so that thepressure difference between the two sides is 3 mmH₂O or less, andpreferably 1 mmH₂O or less, by increasing the diameter of the chamberexhaust tube or employing the method of aspiration from the exhausttube. Oxygen concentration can be measured using a gas chromatographwith a thermal conductivity detector; it can also be simple to use azirconia electrode oximeter. Moreover, in the case of measuring oxygenconcentration with a gas chromatograph using the constitution in FIG. 2,the length of the purge line 21 and aspiration rate of the sampling gasare considered in order that there be no mixing with or aspiration ofoutside air from the purge line 21. In any event, it is necessary tooperate the apparatus so that no large pressure difference occursbetween the outside air pressure and the pressure within the diffuserchamber. The gas permeable packing material which is the subject ofmeasurement in the present invention includes packing materials havingpores through which gas diffuses, regardless of the quantity ofventilation. Usually, the pores have equivalent diameters of 1 mm orless. This term includes any packing material which is the subject ofmeasurement in the present invention, even this is a material which isgenerally called a film, sheet, or membrane, so long as it has poreswith equivalent diameters of 1 mm or less and is gas permeable.Consequently, no restrictions are applied to the form of the pores, thethickness, or type of gas permeable packing material.

Moreover, “equivalent diameters” means-the area of a hole, expressed asthe diameter of a round hole, for the pores which may be elliptical,square, slit, or triangular. Gas permeable packing materials havingpores with equivalent diameters of 1 mm or more may also be the subjectof measurement in the present invention. In that case, however, themeasured value of oxygen diffusing capacity may be incorrect due to theexpansion of hole diameters due to a flow of oxygen which is not aresult of diffusion from the atmosphere side into the chamber, or a flowof nitrogen from the chamber to the atmosphere side.

The method and apparatus for measuring oxygen diffusing capacityrelating to the present invention can measure the quantity ofventilation, with good precision and regardless of the form and size ofthe pores, as the oxygen diffusing capacity. Specifically, the presentinvention can measure with good precision materials having relativelarge holes with equivalent diameters of 0.03-0.5 mm, such as thefollowing: gas permeable packing material comprising a non-gas permeablefilm having holes formed mechanically using pin-like protrusions, asmeans for providing gas permeability to the gas permeable packingmaterial; gas permeable packing material with pores punched in a mold;or a gas permeable packing material wherein holes are formed when partof a film or membrane is melted with the application of electricaldischarge or a heated item with pin-like protrusions. Also, the presentinvention can measure with good precision and in a short period of timea gas permeable packing material which is made as follows: calciumcarbonate or barium sulfate is blended in synthetic polyolefine resinsuch as polyethylene or polypropylene; this is extruded to form a film;then a large number of pores with equivalent diameters of 10 μm or lessare formed by uniaxial drawing or biaxial drawing. Otherwise, thepresent invention can also measure with good precision and in a shortperiod of time a gas permeable packing material, wherein the gaspermeability of nonwoven fabric, comprising heat-fusible syntheticfibers such as polyethylene or polypropylene, is limited bythermocompression bonding.

The gas permeability of these gas permeable packing materials, withoutfurther processing or when applied to nonwoven fabric and formed into agas permeable packing material for a heating packet, can be measuredwith the present invention. The apparatus and method for measuring theoxygen diffusing capacity relating to the present invention can measure,as oxygen diffusing capacity, the gas permeability of gas permeablewallpaper, gas permeable packing material for oxygen scavengers, orapparel which is gas permeable but impermeable to water, as well as thegas permeable packing material for heating packets. Furthermore, thepresent invention can also measure the quantity of ventilation ofmaterials having a fine fibrile structure and comprising drawn film ortubes of polyfluoroethylene resin.

In the case of measuring the quantify of ventilation for gas permeablepacking materials for heating packets in particular, the presentinvention is a very useful measurement method because measurements aremade under conditions similar to those conditions under which theheating packet is actually used. Specifically, when oxygen diffusingcapacity is measured, one surface of the gas permeable packing materialis exposed to the atmosphere. This corresponds to the state wherein theheating packet is in contact with outside air. The other surface isscavenged with nitrogen; this corresponds to the state wherein theconcentration of oxygen within the heating packet is nearly zero.

Consequently, the present invention has applications, as a method formeasuring gas permeability for heating packets, which are not apparentin conventional methods for measuring gas permeability.

Generally, a heating packet is filled with a heat generating compositionwithin a flat, gas permeable inner pouch. While this varies depending onthe type and purpose of heating packet, it is often the case that onesurface of the inner pouch is a gas permeable packing material, whilethe other surface is non-gas permeable packing material.

FIGS. 3-6 show examples of the inner pouches of commercially availableheating packets made with these gas permeable packing materials. FIG.3(b) shows a cross sectional view taken at line 3-3′ in FIG. 3(a). Theseinner pouches are generally made with one surface being gas permeablepacking material and the other surface being non-gas permeable packingmaterial; the edges are heat sealed together to form the flat innerpouch.

The oxygen diffusing capacity of the gas permeable packing material canbe found using the equation 1 with the present invention.

In other words, it is assumed that the quantity of oxygen diffusingthrough the gas permeable packing material into the chamber from theatmosphere is equal to the quantity of nitrogen in the chamber diffusingthrough the gas permeable packing material into the atmosphere. Theoxygen diffusing capacity of the gas permeable packing material is thenfound using the equation 1 from the quantity of nitrogen supplied andthe oxygen concentration in the nitrogen after scavenging.

Oxygen diffusing capacity (Nl/m² 24h)=oxygen concentration((%)/100)×quantity of nitrogen supplied (Nl/h)×24×1/measured area(m²)  [Equation 1]

Moreover, when the pore portion of the measured material is distributedin one portion of the measured surface, appropriate correction of thesurface area makes it possible to find the oxygen diffusing capacity asthe mean oxygen diffusing capacity of the gas permeable packingmaterial. Also, because gas permeability is measured using the quantityof nitrogen supplied to the diffuser and the oxygen concentration in thenitrogen after scavenging, the apparatus and method for measuring oxygendiffusing capacity relating to the present invention can measurequantity of ventilation with good precision and in a short period oftime, regardless of the degree of gas permeability.

When heating packets are designed using gas permeable packing materialswith oxygen diffusing capacity measured in this manner, there is astrong correlation between the quantity of ventilation and the heatingcharacteristics of the heating packet. For this reason, it is very easyto design a heating packet having the desired heating characteristics;moreover, heating packets having stable heating characteristics can bemanufactured.

For example, in the case of producing heating packets wherein the oxygendiffusing capacity of the gas permeable packing material is changed, thesquare (R²: contribution ratio) of the correlation coefficient, betweenthe oxygen diffusing capacity and the rise time, maximum temperature,and continuation time measured with a heating test according to JISS4100, at the point where each approaches linearity becomes 0.85 ormore, preferably 0.90 or more, and more preferably 0.95 or more.

Moreover, the method for measuring oxygen diffusing capacity relating tothe present invention can use another carrier gas (scavenger gas) whichdoes not include oxygen, instead of nitrogen, for scavenging one surfaceof the gas permeable packing material. For example, argon, helium, orcarbon dioxide can be used.

When these gases are substituted for nitrogen gas, the partial pressuredifference of these gases with the atmosphere side becomes markedlylarger than when nitrogen is used. Moreover, depending on the type ofgas, a large quantity of that gas may migrate through to the atmospherebecause the diffusion constant of the gas itself may be high. For thisreason, the quantity of exhaust gas from the measuring chamber maysometimes be less than the quantity of gas supplied. Consequently, theequation 1 cannot be applied without further processing in such cases.

For example, when using helium instead of nitrogen, one must find thecorrect quantity of exhaust gas and substitute this for the quantity ofnitrogen supplied in equation 1. Because the correct quantity of exhaustgas must be found while the partial pressure difference with theatmosphere side is maintained at 1 mmH₂O or less, the structure of theapparatus for measuring oxygen diffusing capacity may become somewhatmore complex than when using nitrogen.

A heating packet is designed with the preferred size and heatingcharacteristics, according to the purpose, area of use, and conditionsof use.

For example, body heating packets, to be applied on the skin of thelower back or shoulders to maintain body temperature, include so-called“regular” heating packets with a relatively large surface area or “mini”heating packets with a small area. These body heating packets withdifferent sizes have variations in their preferred heating capacities;basically, these are designed as heating packets with relatively lowheating values per unit time.

Also, pocket heating packets used in pockets or gloves are designed tohave a relatively high heating values per unit time, because these areused under conditions where temperature retention is poor.

Meanwhile, shoe heating packets have very high heating values per unittime, because these are used under conditions where much heat is lostbecause of contact with water and snow, and because of shoes' poor heatretention.

The gas permeable packing material for body heating packets relating tothe present invention is a gas permeable packing material wherein theoxygen diffusing capacity is usually 1100±220 Nl/m² 24h, preferably1100±150 Nl/m₂ 24h, and more preferably 1100±100 Nl/m² 24h, whenmeasured as follows. Under conditions of 20° C. and 65% relativehumidity, one surface of the gas permeable packing material is exposedto the atmosphere and the other surface is exposed to a flow of nitrogengas at a flow rate of 0.193 Nl/cm² h, in order to scavenge the surfaceof the gas permeable packing material. Meanwhile, the partial pressuredifference between the atmosphere side and the nitrogen gas side is 1mmH₂O or less. With a conventional method for measuring the quantity ofventilation, the fluctuation of the heating characteristics is toogreat, the desired heating capacity cannot be attained, and qualitycontrol for the heating packets is impossible. With the method formeasuring oxygen diffusing capacity relating to the present invention,however, heating packets having the desired heating characteristics areattained, at a higher precision than was possible with the prior art, bythe regulation of the quantity of ventilation as noted above. Moreover,when the gas permeable packing material is used for the entire surfaceof one side of the inner pouch, this quantity of ventilation can be onehalf the aforementioned numerical value in the case where the gaspermeable packing material is used for both sides of the inner pouch andboth sides have equal gas permeability. Also, when used partially, onecan use packing material with the quantity of ventilation calibratedaccording to the percentage of the area.

As noted above, the size of the inner pouch for the “regular type” ofbody heating packet is (90 to 110 mm)×(125 to 145 mm); the size of theinner pouch for the “mini type” is (55 to 75 mm)×(85 to 105 mm).Furthermore, some of these heating packets are 1.5 times, twice, orthree times the size of the regular type. In the present invention,these are all included as body heating packets.

For pocket heating packets relating to the present invention, thequantity of ventilation for the gas permeable packing materialcorresponds to an oxygen diffusing capacity of usually 1600±350 Nl/m²24h, preferably, 1600±220 Nl/m² 24h, and more preferably 1600±150 Nl/m²24h, when measured as follows. Under conditions of 20° C. and 65%relative humidity, one surface of the gas permeable packing material isexposed to the atmosphere and the other surface is exposed to a flow ofnitrogen gas at a flow rate of 0.193 Nl/cm² h, in order to scavenge thesurface of the gas permeable packing material. Meanwhile, the partialpressure difference between the atmosphere side and the nitrogen gasside is 1 mmH₂O or less.

If the oxygen diffusing capability of the packing materials is withinthis range, a heating packet using such packing materials displays verygood heating characteristics. In this instance as well, the quantity ofventilation, in the case when the gas permeable packing material is usedfor all of one side of the inner pouch, can be established with the samemethods as for body heating packets, when maintaining equivalent gaspermeability where the gas permeable packing material is used for all orpart of the inner pouch. For the pocket heating packet relating to thepresent invention, the size of the inner pouch is usually (55 to 75mm)×(85 to 105 mm). However, size is not particularly restricted, solong as the heating packet can be used in pockets or gloves.

For shoe heating packets relating to the present invention, the quantityof ventilation for the gas permeable packing material corresponds to anoxygen diffusing capacity of usually 5500±1100 Nl/m² 24h, preferably5500±800 Nl/m² 24h, and more preferably 5500±500 Nl/m² 24h, whenmeasured as follows. Under conditions of 20° C. and 65% relativehumidity, one surface of the gas permeable packing material is exposedto the atmosphere and the other surface is exposed to a flow of nitrogengas at a flow rate of 0.193 Nl/cm² h, in order to scavenge the surfaceof the gas permeable packing material. Meanwhile, the partial pressuredifference between the atmosphere side and the nitrogen gas side is 1mmH₂O or less. Regulating quantity of ventilation in this manner makesit possible to attain shoe heating packets, having the desired heatingcharacteristics which were difficult to design before now. It is therebypossible to attain a comfortable warm feeling, even when these areinserted in shoes, which generally lose much heat and have poor gaspermeability. Also, the inner pouches of shoe heating packets relatingto the present invention may be in the form of rectangles andtrapezoids, as well as a so-called “horse's hoof” shape which fits inthe toe of a shoe.

The preferred embodiments of the present invention are explained infurther detail on the basis of the following examples; however, thepresent invention is not limited by these.

Examples 1-9

Examples 1-9 are examples relating to the apparatus and method formeasuring oxygen diffusing capacity relating to the present invention.Herein, examples 3-7 are examples of pocket heating packets relating tothe present invention. An apparatus for measuring oxygen diffusingcapacity, identical to that shown in FIGS. 1 and 2, was constructed. Theinstruments were constituted as follows and based on FIGS. 1 and 2.

The chamber 2 of the diffuser 1 is a stainless steel cylinder with aninner diameter of 102 mm and a depth of 37.5 mm; this contains acylindrical partition barrier 7, 25 mm high and with an outer diameterof 60 mm, for preventing the sideways movement of the nitrogen gas. Theinterior volume of the chamber 2 is 285 ml.

In the central portion of the chamber 2, a nitrogen gas supply tube 5,with outer diameter 6.35 m and inner diameter 4.57 mm, is established sothat it extends 15 mm from the bottom surface. Furthermore, an exhausttube 6 is established near the edge inside the chamber.

The frame 8 has a measured surface 12 which is 72 mm×72 mm.

The nitrogen gas flow controller is a mass flow controller (ESTEC Co.,SEK-400MK3).

The oxygen concentration detector 19 is a zirconia electrode oximeter(Toray Engineering, LC-750L) and is constituted to be combined with agas chromatograph 23.

Also, the aspiration pump 25 is an aspiration pump which does not causepulsations.

The gas permeable packing material 4 comprises a non-gas permeablepacking material, of a 50 micron thick polyethylene film laminated to anylon nonwoven fabric (Asahi Chemical Industry, N5051), wherein slitholes are formed in 31 rows at 4 mm intervals within a 32 mm width usinga hole-making apparatus using a rotating blade having pin-likeprotrusions. Also, nine types of gas permeable packing materials withvarying quantities of ventilation are produced by varying the pin holedepth in stages and changing the sizes of the pores. The pores havesizes such that the equivalent diameters are in the range of 0.03 to 0.7mm.

The oxygen diffusing capacities of these nine types of gas permeablepacking material were measured using the aforementioned apparatus formeasuring oxygen diffusing capacity. Measurements were made under thefollowing conditions: temperature of 20° C. and 65% relative humidity, a10 Nl/h (the nitrogen supply is 0.193 Ns/cm² h per unit measured area ofthe gas permeable packing material) supply of nitrogen gas, and samplegas aspiration by the aspiration pump at 1.2 Nl/h. The partial pressuredifference between the atmosphere and the chamber was 1 mmH₂O or less.In addition, the time necessary for the oxygen concentration in thechamber to reach equilibrium was 12 minutes.

Table 1 shows the results.

Next, using the nine types of gas permeable packing material, 97 mm×70mm pouches were produced by back sealing so that the pores weredistributed on one side. These pouches were filled with 20 g of a heatgenerating composition comprising a mixture of 55 wt % of iron powder, 6wt % of activated carbon, 12 wt % of sawdust, 3 wt % of table salt, and24 wt % of water. These were then heat sealed to form nine flat innerpouches as shown in FIG. 6.

These inner pouches were sealed within non-gas permeable other pouchesand made into heating packets.

These nine heating packets were let stand 12 hours in an environmentwith temperature 20° C. and 65% relative humidity and acclimated to thisenvironment. The inner pouches were then removed and the heatingcharacteristics were measured with the test method stipulated in JIS S4100.

The results are shown in Table 1. FIG. 7 shows the relationship betweenoxygen diffusing capacity and maximum temperature (the maximumtemperature reached by the heating packet). FIG. 8 shows therelationship between oxygen diffusing capacity and rise time (timenecessary for the heating packet to reach 40° C. from the start of heatgeneration). FIG. 9 shows the relationship between oxygen diffusingcapacity and continuation time (time from when the heating packetreached 40° C., then reached the maximum temperature, and returned to40° C.). The squares (R²: contribution ratio) of the correlationcoefficient, between the oxygen diffusing capacity and the rise time,maximum temperature, and continuation time, at the point where eachapproaches linearity, were 0.915 for the maximum temperature, 0.922 forthe rise time, and 0.975 for the continuation time. In this way, strongcorrelations of these with oxygen diffusing capacity were confirmed.

TABLE 1 Oxygen diffusing Maximum Continuation capacity temperature Risetime time Example (Nl/m² 24 h) (° C.) (min) (h) 1 1125 52.5 11.5 14.3 21247 55.8 9.8 12.6 3 1710 62.2 7.9 8.0 4 1754 63.5 6.3 7.5 5 1766 61.37.5 7.6 6 1863 65.1 6.2 6.8 7 1882 65.6 6.1 6.4 8 1987 65.8 5.5 5.9 92032 63.7 6.3 6.3

Examples 10-13

Examples 10 to 13 are examples relating to the method for measuringoxygen diffusing capacity and apparatus for measuring oxygen diffusingcapacity relating to the present invention. Among these examples,examples 11 and 12 concern body heating packets relating to the presentinvention. The gas permeable packing material used was four types of gaspermeable packing material (Nitto Denko, BREATHRON), having differentquantities of ventilation and made of porous polyethylene film having alarge number of fine pores with equivalent diameters of 10 μm or lesslaminated to a non-woven nylon cloth. These were measured with the samemethod as in examples 1-9. Next, four types of pouches, 135 mm×100 mm,were prepared as follows. These gas permeable packing materials wereeach used as one surface; a non-gas permeable packing material, ofpolyethylene, nylon nonwoven fabric, polyethylene, adhesive, andreleasing paper laminated together in that order, was used as the othersurface. These packing materials were placed on each other so that thepolyethylene surfaces were in contact and heat sealed on three sides.These four inner pouches were filled with 40 g of a heat generatingcomposition comprising 53 wt % iron powder, 8 wt % activated carbon, 7wt % sawdust, 4 wt % table salt, and 28 wt % water; inner pouches asshown in FIG. 3 were attained. These were then sealed within non-gaspermeable outer pouches to form heating packets.

These pouches underwent the same test of temperature characteristics asdid examples 1-9.

Table 2 shows the results for examples 10-13. FIG. 10 shows therelationship between oxygen diffusing capacity and maximum temperature.FIG. 11 shows the relationship between oxygen diffusing capacity andrise time. FIG. 12 shows the relationship between oxygen diffusingcapacity and continuation time. The squares (R²: contribution ratio) ofthe correlation coefficient, between the oxygen diffusing capacity andthe rise time, maximum temperature, and continuation time, at the pointwhere each approaches linarity, were 0.940 for the maximum temperature,0.974 for the rise time, and 0.985 for the continuation time. In thisway, strong correlations of these with oxygen diffusing capacity wereconfirmed.

TABLE 2 Oxygen diffusing Maximum Continuation capacity temperature Risetime time Example (Nl/m² 24 h) (° C.) (min) (h) 10 1567 68.6 6.4 8.7 111310 62.1 8.5 12.3 12 988 51.6 15.0 18.8 13 677 49.7 18.0 22.0

Examples 14-21

Examples 14 to 21 are examples relating to the method for measuringoxygen diffusing capacity and apparatus for measuring oxygen diffusingcapacity relating to the present invention. These examples 14 and 21concern body heating packets relating to the present invention.

The gas permeable packing material used was eight types of gas permeablepacking material (Nitto Denko, BREATHRON), having different quantitiesof ventilation and made of porous polyethylene film having a largenumber of fine pores with equivalent diameters of 10 μm, or lesslaminated to a non-woven woven nylon cloth. These were measured with thesame method as in examples 1-9. Next, eight types of pouches, 135 mm×100mm, were prepared as follows. These gas permeable packing materials wereeach used as one surface; a non-gas permeable packing material, ofpolyethylene, nylon nonwoven fabric, polyethylene, adhesive, andreleasing paper laminated together in that order, was used as the othersurface. These packing materials were placed on each other so that thepolyethylene surfaces were in contact and heat sealed on three sides.

These eight inner pouches were filled with 34 g of a heat generatingcomposition comprising 53 wt % iron powder, 8 wt % activated carbon, 7wt % sawdust, 4 wt % table salt, and 28 wt % water; inner pouches asshown in FIG. 3 were prepared. These were then sealed within non-gaspermeable outer pouches to form heating packets.

The heating characteristics of these heating packets were examined inthe same way as were examples 1-9.

The results are shown in Table 3. FIG. 13 shows the relationship betweenoxygen diffusing capacity and maximum temperature. FIG. 14 shows therelationship between oxygen diffusing capacity and rise time. FIG. 15shows the relationship between oxygen diffusing capacity andcontinuation time. The squares (R²: contribution ratio) of thecorrelation coefficient, between the oxygen diffusing capacity and therise time, maximum temperature, and continuation time, at the pointwhere each approaches linearity, were 0.968 for the maximum temperature,0.887 for the rise time, and 0.961 for the continuation time. In thisway, strong correlations of these with oxygen diffusing capacity wereconfirmed.

TABLE 3 Oxygen diffusing Maximum Continuation capacity temperature Risetime time Example (Nl/m² 24 h) (° C.) (min) (h) 14 1042 54.7 10.3 15.215 1148 58.4 9.0 12.5 16 1005 53.2 10.5 15.2 17 1185 58.9 8.9 12.2 181222 31.9 8.0 9.9 19 1319 63.0 7.9 8.6 20 1273 63.4 7.0 8.9 21 1315 63.77.7 9.0

Examples 22-28

Examples 22-28 are examples of shoe heating packets relating to thepresent invention.

Seven types of gas permeable packing material were prepared; these hadoxygen diffusing capacities of 4800-6300 Nl/m² 24h and comprised nylonnonwoven fabric with a basis weight of 50 g/m² laminated to 100 μm thickpolyethylene porous film with pores having a maximum diameter of 1.1 μm.These seven types of gas permeable packing materials were placed incontact with sheets of nylon nonwoven fabric with a basis weight of 50g/m² laminated to 50 μm thick polyethylene film, in such a manner thatthe polyethylene surfaces of each were in contact. These were cut in theshape of a horse's hoof, 8.8 cm long and 6.6 cm wide. The edges wereheat sealed to form pouches. These pouches were filled with 14 g of aheat generating composition comprising 66.4 wt % iron powder, 6.4 wt %activated carbon, 1.5 wt % sodium chloride, 22.2 wt % water, 3.1 wt %pearlite powder, and 0.4 wt % highly hydrophilic resin; inner poucheswere prepared.

These inner pouches were then sealed within non-gas permeable outerpouches to form shoe heating packets. These were let stand for one weekat 25° C.

These inner pouches were removed from the outer pouches. The shoeheating packets, having two sheets of gauze above and below, were placedon an aluminum panel and 4 mm thick rubber panel, layered in that orderon a styrene foam, at a temperature of 20° C. The shoe heating packetswere packed with three sheets of rubber and then two sheets of flannel.The heating characteristics were then measured. Table 4 shows theresults.

The squares (R²: contribution ratio) of the correlation coefficient,between the oxygen diffusing capacity and the rise time, maximumtemperature, and continuation time, at the point where each approacheslinearity, were 0.930 for the maximum temperature, 0.966 for the risetime, and 0.982 for the continuation time. In this way, strongcorrelations of these with oxygen diffusing capacity were confirmed.Moreover, the inner pouches of the shoe heating packets in example 23and example 24 were inserted in work shoes with the gas permeablesurface upwards; adult males engaged in light work in an environmentwith a 5° C. outside temperature. As a result, it was found that theseboth maintained comfortable temperatures.

TABLE 4 Oxygen diffusing Maximum Continuation capacity temperature Risetime time Example (Nl/m² 24 h) (° C.) (min) (h) 22 4800 40.5 14.0 7.5 235600 41.5 10.5 6.2 24 6000 42.5 8.6 5.4 25 5800 42.0 9.6 6.0 26 595042.5 9.0 5.6 27 5830 42.0 9.0 6.0 28 6300 43.5 6.0 5.0

comparison examples 1-8

The water vapor transmission of the same eight types of gas permeablepacking material used in examples 14-21 was measured using the methodstipulated in JIS Z 0208. Table 5 shows the results. Since these gaspermeable packing materials were the same as the packing materials inexamples 14-21, water vapor transmission could be correlated with theheating test results for examples 14-21. FIG. 16 shows the relationshipbetween water vapor transmission and maximum temperature. The data inFIG. 16 confirm that maximum temperature changes greatly, even thoughthe difference in water vapor transmission is low in the sectioncontaining the low values for water vapor transmission. Also, thesquares (R²: contribution ratio) of the correlation coefficient, betweenwater vapor transmission and the rise time, maximum temperature, andcontinuation time, at the point where each approaches linearity, were0.641 for the maximum temperature, 0.617 for the rise time, and 0.684for the continuation time. In this way, it was found that thecorrelation between heating characteristics and water vapor transmissionwas very weak.

TABLE 5 Water vapor transmission Comparison example g/m² day 1 230.8 2241.3 3 227.7 4 238.2 5 250.5 6 428.6 7 417.9 8 417.0

Comparison example 9

The gas permeable packing material was prepared by forming 31 rowswithin a width of 32 mm of slit-shaped holes, at intervals of 4 mm, in anon-gas permeable packing material of nylon nonwoven fabric (AsahiChemical Industry, N5051) laminated to 50 micron thick polyethylenefilm, using a hole making device with a rotary blade having pin-likeprotrusions. The pores formed in this manner had equivalent diameters of0.1-0.15 mm. The gas permeability of this gas permeable packing materialwas 7 sec/100 ml, as measured with the Gurley gas permeability testerstipulated in JIS P 8117. This gas permeable packing material was usedas one surface and a non-gas permeable packing material, comprisingpolyethylene, adhesive, and releasing paper laminated together in thatorder, was used as the other surface. A 96 mm×70 mm pouch was formed byplacing these materials together with the polyethylene surfaces incontact and then heat sealing three sides. The pouch was filled with 13g of a heat generating composition comprising 53 wt % iron powder, 8 wt% activated carbon, 7 wt % sawdust, 4 wt % table salt, and 28 wt %water. The pouch was heat sealed to form flat inner pouches. This wasthen sealed within a non-gas permeable outer pouch.

The heating characteristics of the heating pouch were measured in thesame way as example 1-9. Table 6 shows the results.

Comparison Example 10

The gas permeability of the same gas permeable packing material used inexample 11 was 12000 sec/100 ml as measured using the Gurley gaspermeability measuring instrument stipulated in JIS P 8117. This gaspermeable packing material was used as one surface and a non-gaspermeable packing material, comprising polyethylene, adhesive, andreleasing paper laminated together in that order, was used as the othersurface. A 96 mm×70 mm pouch was formed by placing these materialstogether with the polyethylene surfaces in contact and then heat sealingthree sides. The pouch was filled with 13 g of a heat generatingcomposition comprising 53 wt % iron powder, 8 wt % activated carbon, 7wt % sawdust, 4 wt % table salt, and 28 wt % water. The pouch was heatsealed to form flat inner pouches. This was then sealed within a non-gaspermeable outer pouch.

The heating characteristics of the heating pouch were measured in thesame way as example 1-9. Table 6 shows the results. The heatingcapacities were similar, regardless of the great difference betweencomparison example 9 and the Gurley gas permeability.

TABLE 6 Gurley gas Maximum Continuation Comparison permeabilitytemperature Rise time time example (sec/100 ml) (° C.) (min) (h) 9 759.1 6.6 10.5 10 12000 58.2 6.6 11.5

INDUSTRIAL APPLICABILITY

The method for measuring oxygen diffusing capacity and apparatus formeasuring oxygen diffusing capacity relating to the present inventionmake it possible to measure the gas permeability of the gas permeablepacking material quickly and with good precision; the measured value ofoxygen diffusing capacity correlates strongly to heatingcharacteristics. In other words, (1) the present invention can findoxygen diffusing capacity in a short period of time, regardless of porediameter sizes. (2) Even for different types of gas permeable packingmaterials, the measured values of oxygen diffusing capacity correlate toheating characteristics and can be compared without further processing.(3) For these reasons, the design and quality control for heatingpackets becomes easy. And (4) it becomes possible to establish thedesired heating characteristics with a high level of precision bystipulating with oxygen diffusing capacity the gas permeable packingmaterial for body heating packets, pocket heating packets, or shoeheating packets.

The heating packets relating to the present invention (1) are heatingpackets having optimal heating characteristics for a variety of uses,such as body heating packets, pocket heating packets, or shoe heatingpackets. The heating packets relating to the present invention (2) haveheating characteristics corresponding to the various uses as bodyheating packets, pocket heating packets, or shoe heating packets, evenfor varying pore diameters and types of gas permeable packing materials.The heating packets relating to the present invention (3) are shoeheating packets with superior and never before seen temperaturecharacteristics.

What is claimed is:
 1. A method for measuring oxygen diffusing capacityof gas permeable packing materials comprising the steps of: exposing onesurface of a gas permeable packing material to uncontrolled, fresh airfrom the atmosphere; scavenging the opposite surface with a carrier gaswhich does not include oxygen; and measuring the gas permeability of thegas permeable packing material from the concentration of oxygen gas insaid carrier gas after scavenging.
 2. The method for measuring oxygendiffusing capacity according to claim 1, wherein said carrier gas isnitrogen gas.
 3. The method for measuring oxygen diffusing capacityaccording to claim 1, wherein the total pressure difference of theatmospheric pressure and carrier gas pressure contacting the gaspermeable packing material is 3 mmH₂O or less.
 4. The method accordingto claims 1-3, wherein the flow rate of said carrier gas is 50-2000ml/cm²·h per unit measured area of the gas permeable packing material.5. The method according to claim 4, wherein the flow rate of the carriergas is 100-500 ml/cm²·h.
 6. A heating packet comprising: a heatgenerating composition, which generates heat when in contact with theoxygen in air, stored within a gas permeable inner pouch and furthersealed within a non-gas permeable outer pouch, wherein one surface ofthe inner pouch is a gas permeable packing material with an oxygendiffusing capacity measured according to the method of claim
 1. 7. Aheating packet according to claim 6, wherein said heating packet is abody heating packet, wherein said gas permeable packing material has anoxygen diffusing capacity corresponding to a range of 1100±220 Nl/m² 24h measured when one surface of said gas permeable packing material isexposed to the atmosphere and the other surface is scavenged with acarrier gas, not including oxygen, at a flow rate of 0.193 Nl/cm² h perunit area of the gas permeable packing material.
 8. A heating packetaccording to claim 6, wherein said heating packet is a pocket heatingpacket, wherein said gas permeable packing material has an oxygendiffusing capacity corresponding to a range of 1600±350 Nl/m² 24 hmeasured when one surface of said gas permeable packing material isexposed to the atmosphere and the other surface is scavenged with acarrier gas, not including oxygen, at a flow rate of 0.193 Nl/cm² h perunit area of the gas permeable packing material.
 9. A heating packetaccording to claim 6, wherein said heating packet is a shoe heatingpacket, wherein said gas permeable packing material has an oxygendiffusing capacity corresponding to a range of 5500±1100 Nl/m² 24 hmeasured when one surface of said gas permeable packing material isexposed to the atmosphere and the other surface is scavenged with acarrier gas, not including oxygen, at a flow rate of 0.193 Nl/cm² h perunit area of the gas permeable packing material.
 10. The heating packetsaccording to claims 7-9, wherein said carrier gas is nitrogen gas. 11.An apparatus for measuring oxygen diffusing capacity of gas permeablepacking materials comprising a diffuser wherein one surface of a gaspermeable packing material is exposed to uncontrolled, fresh air fromthe atmosphere; the opposite surface is scavenged with a carrier gaswhich does not include oxygen; and oxygen gas in the atmosphere diffusesthrough the gas permeable packing material to the side toward thecarrier gas.
 12. The apparatus for measuring oxygen diffusing capacityaccording to claim 11, wherein said carrier gas is nitrogen gas.
 13. Theapparatus for measuring oxygen diffusing capacity according to claim 11,wherein the diffuser comprises at least one carrier gas supply tube andat least one exhaust tube.
 14. The apparatus for measuring oxygendiffusing capacity according to claim 11, comprising an oxygenconcentration detector inside the chamber of the diffuser and/or via theexhaust tube of the diffuser.
 15. The apparatus for measuring oxygendiffusing capacity according to claim 11, wherein an exhaust pump isconnected to the exhaust tube.
 16. The apparatus according to claims11-15, wherein the flow rate of said carrier gas is 50-2000 ml/cm²·h perunit measured area of the gas permeable packing material.
 17. Theapparatus according to claim 16, wherein the flow rate of the carriergas is 100-500 ml/cm²·h.